In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Certain parts, such as resistive heating elements in furnaces, are a consumable—over time, the parts fail for various reasons, such as oxidation of the materials from which they are made, and must be replaced. Unpredicted or unexpected failure of parts such as resistive heating elements is disruptive to operations. For example, if a failure occurs during operation, i.e., a semiconductor processing operation, the products in the furnace may be ruined and the investment in that product wasted. Also, a furnace with a failed resistive heating element must be cooled down for repair, impacting throughput and operational efficiencies.
Previously, lifetimes of consumable parts were estimated based on several methods.
One prior method visually inspected the consumable part, such as a resistive heating element, on a periodic basis. However, if deterioration occurs between inspection intervals, then the consumable part fails before the next inspection. Also, visual inspection usually requires the larger piece of equipment, such as a furnace, or the production operation, such as semiconductor processing, to be cooled down to room temperature with attendant impacts on productivity.
Another prior method tracks total operating hours of the equipment incorporating the consumable part, such as a furnace incorporating a resistive heating element. However, tracking total run hours does not discriminate between operation at various temperatures or temperature ranges.
For example, resistive heating elements deteriorate at different rates depending on operating temperature. Customers typically have several furnaces operating with different conditions as different times. Batch processes operate at various temperatures during one processing cycle. Simply counting total operating hours does not account for these variations and the variations' different impacts on operating lifetime.
A further prior method uses an empirical approach, running equipment until the consumable part fails and then setting a preventive maintenance schedule based on that observed failure time. The preventive maintenance schedule includes exchange of all consumable parts typically at a time period shorter than the observed time to failure. However, setting a preventive maintenance schedule in this manner is not an optimum solution. Such a preventive maintenance schedule is usually based on shortest life expectancy and an optional margin of error, without any consideration of the actual utilization. Thus, useable operating life remains when the preventive maintenance schedule is enacted, often a large amount of life time because consideration of differing temperatures during the use period has not been made.